The present invention generally relates to rollover sensors and, more particularly, to vehicle rollover detection with reduced sensor hardware for sensing a rollover condition of a vehicle.
Increasingly, automotive vehicles are employing safety-related devices that deploy in the event that the vehicle experiences a rollover so as to provide added protection to the occupants of the vehicle. For example, upon detecting a vehicle rollover condition, a pop-up roll bar can be deployed such that, when activated, the roll bar further extends vertically outward to increase the height of support provided by the roll bar during a rollover event. Other controllable features may include deployment of one or more airbags, such as frontal airbags, side mounted airbags, and roof rail airbags, or actuating a pretensioner to pretension a restraining device, such as a seatbelt or safety harness, to prevent occupants of the vehicle from ejecting from the vehicle or colliding with the roof of the vehicle during a rollover event.
In the past, mechanical-based rollover sensors have been employed in automotive vehicles to measure the angular position of the vehicle from which a rollover condition can be determined. The mechanical sensors have included the use of a pendulum normally suspended vertically downward due to the Earth""s gravitational force. Many mechanical automotive sensing devices are employed simply to monitor the angular position of the vehicle relative to a horizontal level ground position. As a consequence, such mechanical automotive sensors have generally been susceptible to error when the vehicle travels around a corner or becomes airborne, in which case the Earth""s gravitational force, which the sensor relies upon, may be overcome by other forces.
More sophisticated rollover sensing approaches require the use of as many as six sensors including three accelerometers and three angular rate sensors, also referred to as gyros, and a microprocessor for processing the sensed signals. The three accelerometers generally provide lateral, longitudinal, and vertical acceleration measurements of the vehicle, while the three gyros measure angular pitch rate, roll rate, and yaw rate. However, such sophisticated rollover sensing approaches generally require a large number of sensors which add to the cost and complexity of the overall system. In addition, known sophisticated systems are generally susceptible to cumulative drift errors, and therefore occasionally must be reset.
In an attempt to minimize the number of sensors required, conventional sensing approaches have employed, at a minimum, both an angular rate sensor and an accelerometer. For those sensors designed to detect both rollover and pitchover events, a second angular rate sensor and a second accelerometer are typically added. While the angular rate sensor can be integrated to calculate a roll angle, in practice, angular rate sensors typically generate a non-zero, time-varying output, even in the absence of a roll rate. This bias may cause a significant error in the integration-generated roll angle, and such bias must be compensated in order to provide an accurate sensed measurement. Accordingly, conventional rollover sensing approaches typically require auxiliary sensors, in lieu of the single angular rate sensor, to compensate for zero-input biases inherent in many angular rate sensors.
Accordingly, it is desirable to provide for an accurate and timely rollover detection apparatus and method that minimizes the number of sensors that are required to detect rollover and/or pitchover of the vehicle. More particularly, it is desirable to provide for a rollover detection apparatus and method that allows for use of an angular rate sensor, without requiring auxiliary sensors in addition thereto. It is further desirable to provide for the removal of signal bias and noise associated with sensed signals generated by a sensor, such as an angular rate sensor.
In accordance with the teachings of the present invention, a vehicle rollover sensing apparatus and method are provided for detecting an anticipated overturn condition of the vehicle and providing timely deployment of safety-related devices. The rollover sensing apparatus includes an angular rate sensor for sensing attitude rate of change of a vehicle and producing an output signal indicative thereof. The rollover sensing apparatus also has an integrator for integrating the sensed attitude rate of change signal and producing an attitude angle. According to one aspect of the present invention, the integrator has a variable time window. The rollover sensing apparatus further includes a comparator for comparing the attitude angle and attitude rate of change to threshold values, and an output for deploying a vehicle overturn condition signal based on the comparison. According to another aspect of the present invention, the comparator includes a gray-zone deployment indicator.
A method is also provided for detecting an anticipated overturn condition of a vehicle. The method includes the steps of sensing the attitude rate of change of a vehicle and producing an output signal indicative thereof, integrating the sensed attitude rate of change signal during a time window to generate an attitude angle, comparing the attitude angle and attitude rate of change to threshold values, and deploying an output signal based on the comparison. According to one aspect of the present invention, the time window is variable. According to a further aspect of the present invention, the comparison is compared to a gray-zone indicator.
According to a further aspect of the present invention, a bias removal device is provided for removing bias from a sensed signal, such as a sensed rate signal. The bias removal device includes an input for receiving a sensed signal from a sensor, a high pass filter for filtering the sensed signal when the sensed signal has an amplitude below a first threshold, an all pass region for passing the sensed signal when the sensed signal has an amplitude above the first threshold, and an output for providing a bias removed output signal.
Accordingly, the rollover sensing apparatus and method of the present invention advantageously minimizes the number of sensors that are required to detect an overturn (rollover and/or pitchover) condition of a vehicle. It should be appreciated that the apparatus and method employ an angular rate sensor, without requiring other auxiliary sensors, to achieve cost efficient and accurate rollover detection. It should further be appreciated that the adaptive bias removal allows for enhanced accuracy with an angular rate sensor, without requiring use of auxiliary sensors.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.